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  <title>Document</title>
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  <script>
    let num=+prompt('请输入成绩')
    if (num>90){
      alert('优秀')
    }
    else if(num>=70){
      alert('良好')
    }
    else if(num>=60){
      alert('及格')
    }
    else {
      alert('不及格')
    }
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